The present invention relates to a miniature motor in which a brush holder for holding a brush is directly attached to a brush holder attaching portion arranged in a gear case.
Concerning this type miniature motor, the miniature motor having a reduction gear mechanism shown in FIGS. 19 to 28 is provided. (For example, refer to Patent Document 1.)
As shown in FIGS. 19 to 21, this miniature motor 1 includes: a yoke (motor case) 2 made of metal, the shape of which is substantially cylindrical, one end side of which is open; and a gear case 5 made of synthetic resin which is fastened and fixed to a flange portion 2b, which is formed round an opening end 2a of the yoke 2, via the screws 2e. 
As shown in FIG. 19, a pair of magnets 3, 3 are bonded onto the inner circumferential face 2c of the yoke 2 with adhesive. The armature shaft 11 is pivotally supported by the bearing 4a which is engaged with the cylindrical portion 2d having a bottom portion arranged at the other end of the yoke 2, and by the bearings 4b, 4c engaged with the neighborhoods of both end portions of the shaft hole 6 of the gear case 5.
The worm 12 is formed in the neighborhood of the forward end portion 11a of the armature shaft 11. The armature 10 is attached to a position on the armature shaft 11 opposing to a pair of magnets 3, 3. This armature 10 is fixed to the neighborhood of the base end portion 11b of the armature shaft 11. The armature 10 includes: an armature core 10a having a coil winding portion, the number of the slots of which is predetermined; and an armature coil 10b wound round the coil winding portion of this armature core 10a. 
The commutator 13 is fixed at a position on the armature shaft 11 opposing to the boundary portion with the yoke 2 and the gear case 5. This commutator 13 has commutator pieces 13a, the number of which is the same as that of the coil winding portions of the armature core 10a. Each commutator piece 13a of the commutator 13 and the armature coil 10b of the armature 10 are electrically connected to each other. An opening end portion of the shaft hole 6 of the gear case 5 is formed into the large diameter hole portion 6a. At the position of this large diameter hole portion 6a opposing to the commutator 13, a pair of brush holder attaching portions 7, 7′ are integrally formed. The shape of each brush holder attaching portion is formed into a recess shape. In these brush holder attaching portions 7, 7′ and the cutout portions 8, 8′, the brush holders 20, 20′, which are made of metal such as brass, for holding the brush 17 are attached by means of press-fitting.
As shown in FIGS. 19 and 20, in the shaft hole 6 of the gear case 5, the recess-shaped reduction gear mechanism housing portion 9 is formed so that it can be communicated with the shaft hole 6. In this recess-shaped reduction gear mechanism housing portion 9, the wheel gear 14, which is meshed with the worm 12 of the armature shaft 11, is pivotally supported via the bearing 16. The worm 12 and the wheel gear 14 form the reduction gear mechanism S. The output shaft 15 is integrally protruded from the center of the wheel gear 14. This output shaft 15 is protruded outside from the gear case 5.
As shown in FIGS. 19 and 21 to 25, one brush holder 20 of the pair of brush holders 20, 20′ includes: a brush box portion 20a made of metal such as brass for housing the brush 17; a first connecting terminal piece portion 20b, which is formed being vertically bent at the upper center of the brush box portion 20a, connected with the pigtail 18 formed integrally with the brush 17; and a second connecting terminal piece portion 20c, which is formed being bent at one side end of the brush box portion 20a so that it can cover the rear side opening portion of the brush box portion 20a. 
The brush box portion 20a of one brush holder 20 is press-fitted into the recess-shaped brush holder attaching portion 7 of the gear case 5, and the second connecting terminal piece 20c of the brush holder 20 is press-fitted into the cutout portion 8. In this case, the forward end portion 20d, which is vertically bent, of the second connecting terminal piece portion 20c is connected to the control circuit on the circuit board not shown in the drawing.
As shown in FIGS. 19, 21, 22 and 26 to 28, the other brush holder 20′ of the pair of brush holders 20, 20′ includes: a brush box portion 20a made of metal such as brass for housing the brush 17; a first connecting terminal piece portion 20b, which is vertically bent at the center of the upper portion of this brush box portion 20a, connected with the pigtail 18 formed integrally with the brush 17; and a second connecting terminal piece portion 20c′ which is formed being bent at one side end of the brush box portion 20a so that it can cover the rear side opening portion of the brush box portion 20a. The second connecting terminal piece portion 20c′ of the other brush holder 20′ is shorter than the second connecting terminal piece portion 20c of one brush holder 20.
The brush box portion 20a of the other brush holder 20′ is press-fitted into the recess-shaped brush holder attaching portion 7′ of the gear case 5, and the second connecting terminal piece portion 20c′ of the other brush holder 20′ is press fitted into the cutout portion 8′. In this case, the forward end portion 20d of the second connecting terminal piece portion 20c′ is connected to the control circuit on the circuit board not shown.
Each brush 17, which is exposed outside from the front side opening portion of each brush box portion 20a of the pair of brush holders 20, 20′, is pushed by the compressive coil spring 19 so that the brush 17 can be contacted with the commutator 13. As described before, each brush 17 is electrically connected to the control circuit on the circuit board not shown via each forward end portion 20d of the second connecting terminal piece portion 20c, 20c′ of each brush holder 20, 20′. When each switch of the pair of switches of this control circuit is switched from OFF to ON, an electric current flows in the armature 10 and others, so that the armature shaft 11 can be rotated normally and reversely.
[Patent Document 1]
JP-A-2002-159154
However, in the conventional miniature motor 1 described above, the entire brush holder 20, 20′ for holding the brush 17 is made of metal such as brass. Accordingly, the weight of the miniature motor 1 is increased and further the manufacturing cost is raised. Furthermore, the brush 17 coming into contact with the commutator 13 arranged on the rotating armature shaft 11 vibrates in the brush box 20a of each brush holder 20, 20′ made of metal. Accordingly, operational noise tends to be generated.